REST API calls with Invoke-RestMethod in PowerShell

Introduction

Invoke-RestMethod helps you talk to web services easily. It sends requests and gets data back in a simple way.

You want to get weather information from an online service.

You need to send data to a website to create or update something.

You want to fetch user details from a web API.

You want to automate checking your online account balance.

You want to download data from a public API for analysis.

Syntax

PowerShell

Invoke-RestMethod -Uri <string> [-Method <string>] [-Headers <hashtable>] [-Body <string>] [-ContentType <string>]

-Uri is the web address you want to call.

-Method is usually GET (to get data) or POST (to send data).

Examples

Simple GET request to get data from the API.

PowerShell

Invoke-RestMethod -Uri 'https://api.example.com/data'

Send JSON data with a POST request.

PowerShell

Invoke-RestMethod -Uri 'https://api.example.com/data' -Method POST -Body '{"name":"John"}' -ContentType 'application/json'

GET request with an authorization header.

PowerShell

Invoke-RestMethod -Uri 'https://api.example.com/data' -Headers @{Authorization='Bearer token123'}

Sample Program

This script calls a public API to get a post's details and prints the title and body.

PowerShell

try {
  $response = Invoke-RestMethod -Uri 'https://jsonplaceholder.typicode.com/posts/1'
  Write-Output "Title: $($response.title)"
  Write-Output "Body: $($response.body)"
} catch {
  Write-Output "Error calling API: $_"
}

Important Notes

Invoke-RestMethod automatically converts JSON responses into PowerShell objects.

Use try/catch to handle errors like network issues.

Always check the API documentation for required headers and methods.

Summary

Invoke-RestMethod makes calling web APIs simple and returns easy-to-use objects.

You can use it to GET data or POST data with headers and body.

Handling errors helps keep your scripts reliable.

Practice

1. What does the PowerShell cmdlet Invoke-RestMethod primarily do?

easy

A. It sends HTTP requests to web APIs and returns parsed responses.

B. It creates new files on the local system.

C. It compiles PowerShell scripts into executables.

D. It manages Windows services remotely.

Solution

1. Step 1: Understand the purpose of Invoke-RestMethod

   This cmdlet is designed to send HTTP requests to REST APIs and automatically parse the response into PowerShell objects.

2. Step 2: Compare options with the cmdlet's function

   Options B, C, and D describe unrelated tasks like file creation, compiling, or service management, which Invoke-RestMethod does not perform.

3. Final Answer:

   It sends HTTP requests to web APIs and returns parsed responses. -> Option A

4. Quick Check:

   Invoke-RestMethod = Sends HTTP requests [OK]

Hint: Invoke-RestMethod calls APIs and returns objects [OK]

Common Mistakes:

• Confusing Invoke-RestMethod with file or service commands
• Thinking it only sends GET requests
• Assuming it returns raw text instead of parsed objects

2. Which of the following is the correct syntax to send a GET request to https://api.example.com/data using Invoke-RestMethod?

easy

A. Invoke-RestMethod -Url https://api.example.com/data -Method GET

B. Invoke-RestMethod -Url https://api.example.com/data -Method POST

C. Invoke-RestMethod -Uri https://api.example.com/data -Method FETCH

D. Invoke-RestMethod -Uri https://api.example.com/data -Method GET

Solution

1. Step 1: Identify correct parameter names and HTTP method

   The correct parameter for the URL is '-Uri' and the HTTP method for retrieving data is 'GET'.

2. Step 2: Check each option for syntax correctness

   Invoke-RestMethod -Uri https://api.example.com/data -Method GET uses '-Uri' and '-Method GET' correctly. Invoke-RestMethod -Url https://api.example.com/data -Method POST uses '-Url' (incorrect parameter) and POST method. Invoke-RestMethod -Url https://api.example.com/data -Method GET uses '-Url' (incorrect parameter). Invoke-RestMethod -Uri https://api.example.com/data -Method FETCH uses an invalid HTTP method 'FETCH'.

3. Final Answer:

   Invoke-RestMethod -Uri https://api.example.com/data -Method GET -> Option D

4. Quick Check:

   Use -Uri and -Method GET for GET requests [OK]

Hint: Use -Uri for URL and -Method GET for GET requests [OK]

Common Mistakes:

• Using -Url instead of -Uri
• Using -Method POST instead of GET
• Using invalid HTTP methods like FETCH

3. What will be the output of this PowerShell code snippet?

 $response = Invoke-RestMethod -Uri 'https://jsonplaceholder.typicode.com/posts/1' -Method GET
 $response.title 

medium

A. Null, because $response.title does not exist

B. An error because the -Method parameter is missing

C. The title of the post with ID 1 from the API

D. The entire JSON response as a string

Solution

1. Step 1: Understand Invoke-RestMethod behavior

   Invoke-RestMethod sends a GET request and parses JSON into an object. Accessing $response.title retrieves the 'title' property.

2. Step 2: Analyze the code and expected output

   The API returns a JSON object with a 'title' field for post ID 1. The code prints that title string.

3. Final Answer:

   The title of the post with ID 1 from the API -> Option C

4. Quick Check:

   Invoke-RestMethod parses JSON; access properties directly [OK]

Hint: Invoke-RestMethod returns objects; access properties like .title [OK]

Common Mistakes:

• Expecting raw JSON string instead of parsed object
• Forgetting to specify -Method GET (optional but recommended)
• Assuming $response.title is null without checking API

4. You run this command but get an error:

Invoke-RestMethod -Uri 'https://api.example.com/data' -Method POST -Body '{"name":"John"}'

What is the most likely cause?

medium

A. The -Method POST is invalid; only GET is allowed.

B. The -Body parameter must be a PowerShell object, not a JSON string.

C. The URI is missing the protocol (http/https).

D. Invoke-RestMethod cannot send POST requests.

Solution

1. Step 1: Understand -Body parameter requirements

   Invoke-RestMethod expects the -Body parameter as a PowerShell object or properly formatted string with correct headers.

2. Step 2: Identify issue with JSON string body

   Passing a raw JSON string without setting Content-Type header or converting to object causes errors.

3. Final Answer:

   The -Body parameter must be a PowerShell object, not a JSON string. -> Option B

4. Quick Check:

   Use objects or set headers when sending JSON body [OK]

Hint: Send objects or set headers when posting JSON body [OK]

Common Mistakes:

• Passing JSON string without Content-Type header
• Assuming POST is unsupported
• Omitting protocol in URI

5. You want to send a POST request with JSON data {"username":"admin","password":"pass123"} to https://api.example.com/login using Invoke-RestMethod. Which script correctly sends the request and handles the JSON response?

hard

A. $body = @{username='admin'; password='pass123'}Invoke-RestMethod -Uri 'https://api.example.com/login' -Method POST -Body ($body | ConvertTo-Json) -ContentType 'application/json'

B. $body = '{"username":"admin","password":"pass123"}'Invoke-RestMethod -Uri 'https://api.example.com/login' -Method POST -Body $body

C. $body = @{username='admin'; password='pass123'}Invoke-RestMethod -Uri 'https://api.example.com/login' -Method GET -Body $body

D. Invoke-RestMethod -Uri 'https://api.example.com/login' -Method POST -Body @{username='admin'; password='pass123'}

Solution

1. Step 1: Prepare the body as a PowerShell object and convert to JSON

   Creating a hashtable and converting it to JSON ensures the body is correctly formatted for the API.

2. Step 2: Use -ContentType 'application/json' to inform the server

   Setting the Content-Type header is necessary for the server to interpret the JSON body correctly.

3. Step 3: Verify the HTTP method is POST

   POST is required to send data; GET with body is invalid.

4. Final Answer:

   $body = @{username='admin'; password='pass123'}
   Invoke-RestMethod -Uri 'https://api.example.com/login' -Method POST -Body ($body | ConvertTo-Json) -ContentType 'application/json' -> Option A

5. Quick Check:

   Convert body to JSON and set Content-Type for POST [OK]

Hint: Convert body to JSON and set Content-Type for POST [OK]

Common Mistakes:

• Sending raw JSON string without Content-Type header
• Using GET method with body
• Passing hashtable directly without JSON conversion